Method for producing particulate alumina and composition containing particulate alumina

ABSTRACT

One embodiment of the present invention provides a method for producing a particulate alumina, comprising heat-treating (calcining) a composition comprising alumina, an alumina hydrate, ammonium chloride and a halogen compound other than ammonium chloride and then disintegrating the heat-treated product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is an application filed pursuant to 35 U.S.C. Section 111(a) withclaiming the benefit of U.S. provisional application Serial No.60/479,836 filed Jun. 20, 2003 under the provision of 35 U.S.C. 111(b),pursuant to 35 U.S.C. Section 119(e) (1).

TECHNICAL FIELD

The present invention relates to a method for producing a rounded(roundedly shaped) particulate alumina, more specifically, the presentinvention relates to a production method of a particulate alumina whichis useful, for example, as a sealing material of electronic components,a filler, a finish lapping material or an aggregate of refractories,glasses, ceramics or their composite materials, and also relates to aresin composition and the like using the particulate alumina.

BACKGROUND ART

To cope with recent trend toward the realization of advanced informationtelecommunication represented by multimedia, the electronic componentsused for these devices are required to respond tohigh-speed/high-frequency processing or modularization and a matter ofimportance in the development is, for example, to improve the electricalproperties, such as reduction of dielectric constant. Furthermore, withthe progress of high-integration and high-density packaging ofelectronic components, the power consumption per chip is more and moreincreasing and it is also a matter of importance in the development toefficiently dissipate the heat generated and less elevate thetemperature of the electronic component device. Under thesecircumstances, alumina having excellent thermal conductivity,particularly corundum (α-alumina), is attracting attention as a fillerfor use in an insulating sealing material of semiconductors, a substratematerial on which the components are mounted, or a heat-radiatingspacer, and being used in various fields.

As such a corundum particle, a spherically shaped corundum particlehaving no cutting edge and having an average particle size of 5 to 35 μmhas been proposed, which is obtained by adding aluminum hydroxide aloneor in combination with another known chemical as the crystallizationaccelerator to a ground product of electrofused alumina or sinteredalumina, and calcining it (see, for example, JP-A-5-294613 (the term“JP-A” as used herein means an “unexamined published Japanese patentapplication”)).

In this patent publication, it is stated that in the case of a corundumparticle having an average particle size of 5 μm or less, a particlehaving a rounded shape can be obtained by a known method of adding acrystallization accelerating agent to aluminum hydroxide.

Also, a technique of thoroughly dehydrating and thermally decomposingalumina hydroxide at 700° C. or less at the calcining, then elevatingthe temperature to produce an intermediate calcined material having anα-conversion of 90% or more, and calcining it in the presence of afluorine hardening agent to obtain spherical alumina has been disclosed(see, for example, JP-A-5-43224).

On the other hand, there is known a so-called flame-spraying methodwhere alumina according to the Bayer process is jetted into ahigh-temperature plasma or oxyhydrogen flame and the alumina undermelting is rapidly cooled, thereby forming a rounded crystal particle.In some situations, this method might be unprofitable due to large unitheat consumption, the obtained alumina might contain δ-alumina as aby-product.

As for the corundum particle, ground products of electrofused alumina orsintered alumina are known, but these are both an amorphously shapedparticle having sharp cutting edges and their filling in rubbers orplastics might cause great abrasion of the kneader, shaping die or thelike.

DISCLOSURE OF THE INVENTION

An object of the present invention is to produce a rounded particulatealumina having excellent flowability for use as a filler, for example,in resin such as rubber and plastic or in glass and provide a highlythermally conductive rubber composition, a highly thermally conductiveplastic composition and a ceramic composition each using the particulatealumina.

As a result of intensive investigations to develop a particulate aluminahaving the above-described preferred properties, the present inventorshave found that when a specific composition is baked and disintegrated,a rounded particulate alumina having excellent flowability and lowviscosity can be obtained and this ensures good filling in rubbers,plastics or ceramics. The present invention has been accomplished basedon this finding.

That is, the present invention relates to a method for producingparticulate alumina and to a composition containing particulate aluminaas follows.

(1) A method for producing a particulate alumina, comprisingheat-treating (calcining) a composition comprising alumina, an aluminahydrate, ammonium chloride and a halogen compound other than ammoniumchloride and then disintegrating the heat-treated product.

(2) The production method of a particulate alumina as described in (1)above, wherein the halogen compound other than ammonium chloride is afluorine compound or a boron-fluorine compound.

(3) The production method of a particulate alumina as described in (2)above, wherein the fluorine compound is at least one member selectedfrom the group consisting of AlF₃, NaF, CaF₂, MgF₂ and Na₃AlF₆.

(4) A method for producing a particulate alumina, comprisingheat-treating (calcining) a composition comprising alumina, an aluminahydrate, ammonium chloride and a boron compound and then disintegratingthe heat-treated product.

(5) A method for producing a particulate alumina, comprisingheat-treating (calcining) a composition comprising alumina, an aluminahydrate, ammonium chloride, a halogen compound other than ammoniumchloride, and a boron compound and then disintegrating the heat-treatedproduct.

(6) The production method of a particulate alumina as described in (4)or (5) above, wherein the boron compound is at least one member selectedfrom the group consisting of B₂O₃, H₃BO₃, mNa₂O·nB₂O₃ (m and n eachrepresents an integer of 1 or more, hereinafter the same) and aboron-fluorine compound.

(7) The production method of a particulate alumina as described in anyone of (1) to (6) above, wherein the particulate alumina has a roundedshape having no cutting edge.

(8) The production method of a particulate alumina as described in anyone of (1) to (7) above, wherein the composition is previouslygranulated before heat-treating (calcining) the composition.

(9) The production method of a particulate alumina as described in anyone of (1) to (8) above, wherein the alumina hydrate is at least onemember selected from the group consisting of an aluminum hydroxide, analumina gel and a partially hydrated aluminum compound.

(10) The production method of a particulate alumina as described in anyone of (1) to (9) above, wherein the average particle size of theparticulate alumina is 10 μm or less.

(11) The production method of a particulate alumina as described in (10)above, wherein the average particle size of the particulate alumina isfrom 0.3 to 8 μm.

(12) A resin composition comprising a particulate alumina produced bythe production method described in any one of (1) to (11) above, and apolymer compound.

(13) The resin composition as described in (12) above, wherein thepolymer compound is at least one member selected from an aliphaticresin, an unsaturated polyester resin, an acrylic resin, a methacrylicresin, a vinyl ester resin, an epoxy resin and a silicone resin.

(14) The resin composition as described in (12) or (13) above, whereinthe content of the particulate alumina is 70 mass % of more.

(15) The resin composition as described in any one of (12) to (14)above, wherein the particulate alumina is coated with a surface-treatingagent.

(16) The resin composition as described in (15) above, wherein thesurface-treating agent is a silane coupling agent.

(17) The resin composition as described in (15) above, wherein thesurface-treating agent is a compound having any one or more groupselected from the group consisting of an amino group, a carboxyl groupand an epoxy group.

(18) The resin composition as described in (15) above, wherein thesurface-treating agent is a modified silicone oil.

(19) The resin composition as described in any one of (15) to (18)above, wherein the coverage of the surface-treating agent is from 0.05to 5 mass % based on the particulate alumina.

(20) A ceramic composition comprising a particulate alumina produced bythe production method described in any one of (1) to (11) above.

(21) An electronic component or semiconductor device comprising theresin composition as described in any one of (12) to (19) above.

(22) A CPU or PDP comprising the resin composition as described in anyone of (12) to (19) above.

(23) A peripheral equipment for batteries, or a peltier element, aninverter or a power transistor, comprising the resin composition asdescribed in any one of (12) to (19) above.

DETAILED DESCRIPTION OF INVENTION

The present invention is described in detail below.

The alumina used as a starting material in the present invention is aground product of a calcined alumina produced by a known productionmethod, and the particle size is, in terms of the average particle size,within a range of 0.3 to 8 μm, preferably 1 to 7 μm.

In order to accelerate the rounding of starting material alumina, analumina hydrate (rounding accelerator) is previously mixed with aluminabefore heat treatment.

The alumina hydrate used here may be, for example, an aluminum hydroxidesuch as gibbsite, bayerite, boehmite and diaspore, an amorphous aluminumhydroxide such as alumina gel and pseudo-boehmite, or a partiallyhydrated aluminum compound such as aluminum oxide (alumina) of whichsurface is partially hydrated, but in particular, the alumina hydrate ispreferably an aluminum hydroxide, an alumina gel or a fine particulatealumina having good thermal reactivity.

From the economic point of view, an aluminum hydroxide according to theBayer process (gibbsite) is preferred and its average particle size ispreferably 10 μm or less, most preferably 5 μm or less.

The present inventors have confirmed by observation that this roundingaccelerator acts on alumina synergistically with the other chemicals(additives) described later to selectively react with irregular cuttingedges and thereby round the alumina and at the same time, theagglomerate as the heat-treated product is low in the cohesive force andcan be easily disintegrated into primary particles.

The optimal amount of the rounding accelerator added varies depending onthe particle size of the ground product of alumina, but in the case ofadding an aluminum hydroxide, the amount added is, in terms of alumina,preferably from 5 to 300 mass %, most preferably from 80 to 180 mass %,based on alumina. If the amount added is less than 5 mass %, cuttingedges of the starting material alumina remain and the cohesive force ofthe agglomerate becomes strong, whereas if it exceeds 300 mass %, excessaluminum hydroxide is mixed as a free fine particulate alumina in theproduct and this is not preferred.

As for the chemicals further added, in addition to ammonium chloride, ahalogen compound other than ammonium chloride and/or a boron compound,which are known as the crystal growth accelerator for alumina, are used.Examples of the halogen compound other than ammonium chloride comprise afluorine compound such as AlF₃, NaF, CaF₂, MgF₂ and Na₃AlF₆, and aboron-fluorine compound such as ammonium borofluoride, potassiumborofluoride and sodium borofluoride. Examples of the boron compoundinclude B₂O₃, H₃BO₃ and mNa₂O·nB₂O₃. In particular, a combination use ofa fluorine compound and a boron compound is preferred.

The amount of each chemical added varies depending on the purity of thealumina as starting material, the heating temperature, the residencetime in furnace and the kind of heating furnace and therefore cannot beflatly defined, but, for example, the effective concentration ofammonium chloride added is from 2 to 8 mass %, preferably from 4 to 6mass %, based on the entire alumina content. The ammonium chloride has afunction of more effectively and uniformly causing a reaction for theacceleration of rounding and if the amount added thereof is less than 2mass %, the effect of accelerating the rounding decreases, whereas if itexceeds 8 mass %, an effect attributable to increase in the amount addedis not obtained but rather the uniformity is lost. The amount added ofthe crystal growth accelerator other than ammonium chloride, such asfluorine compound and boron compound (in the case where these twocompounds are used in combination, the total amount), is from 1 to 7mass %, preferably from 3 to 5 mass %, based on the entire aluminacontent. If the amount added of the crystal growth accelerator such asfluorine compound is less than 1 mass %, the effect on the accelerationof crystallization is not obtained, whereas if it exceeds 7 mass %, theacceleration of crystallization is increased only locally, causing largevariations in crystallization.

The composition containing these alumina, alumina hydrate, ammoniumchloride and crystal growth accelerator is mixed and then heated. Atthis time, from the standpoint of enhancing the reaction rate, themixture is preferably granulated before heating.

The mixing method is not particularly limited and may be sufficient ifrespective components can be uniformly mixed, and a method commonlyknown as a powder mixing method can be used. Examples of the methodinclude mixing devices such as rocking blender, Nauter mixer, ribbonmixer, V-shaped blander and Henschel mixer. Other than these, a grindersuch as ball mill and vibrating mill can also be used.

With respect to the kind of the heating furnace for heat-treating(calcining) the mixed composition, a known furnace such as singlefurnace, tunnel furnace and rotary kiln may be used and the heatingtemperature is not particularly limited as long as the final product canbe a-alumina. The heating temperature is usually 1,000° C. or more,preferably from 1,350 to 1,600° C., more preferably from 1,400 to 1,550°C. If the heating temperature exceeds 1,600° C., the cohesive force ofthe agglomerate is increased even in the co-presence of aluminumhydroxide and the agglomerate cannot be easily disintegrated intoprimary particles.

The residence time in the heating furnace varies depending on theheating temperature, but a residence time of 30 minutes or more,preferably on the order of 1 to 3 hours, is necessary.

The particulate alumina prepared by such a method takes the form of asecondary agglomerated particle in many cases and therefore, isdisintegrated in a short time by a known grinding device such as ballmill, vibrating mill and jet mill, whereby a rounded particulate aluminahaving a desired particle size distribution, preferably having anaverage particle size (primary particle) of 10 μm or less, morepreferably from 0.3 to 8 μm, can be obtained.

In the above-described production method, when alumina or aluminumhydroxide reduced in the radioactive element such as uranium or thoriumis used, a rounded particulate alumina having a low α-ray radiantquantity can be produced. In use as a filler for resin sealing of ahigh-integrated IC or the like, the rounded particulate alumina having alow α-ray radiant quantity (0.01 c/cm²·hr) is useful so as to preventthe memory device from erroneous operations (e.g., software error) byα-ray.

The particulate alumina of the present invention is preferably filled inan oil or a polymer compound such as rubber and plastic, and can besuitably used as a highly thermally conductive grease composition, ahighly thermally conductive rubber composition or a highly thermallyconductive plastic composition. In particular, the filling is preferablyperformed to give a particulate alumina content of 70 mass % or more.

The polymer compound constituting the composition of the presentinvention may be a known polymer compound, but preferred examplesthereof include an aliphatic resin, an unsaturated polyester resin, anacrylic resin, a methacrylic resin, a vinyl ester resin, an epoxy resinand a silicone resin.

These resins each may be a low molecular weight polymer or a highmolecular weight polymer or may be in the form of oil, rubber or curedproduct and this may be arbitrarily selected according to the purposefor which the resin is used and the environment.

Examples of the resin include a hydrocarbon-based resin (e.g.,polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylatecopolymer, ethylene-propylene copolymer, poly(ethylene-propylene),polypropylene, polyisoprene, poly(isoprene-butylene), polybutadiene,poly(styrene-butadiene), poly(butadiene-acrylonitrile), polychloroprene,chlorinated polypropylene, polybutene, polyisobutylene, olefin resin,petroleum resin, styrol resin, ABS resin, chroman-indene resin, terpeneresin, rosin resin, diene resin); a (meth)acrylic resin (for example, aresin obtained by homopolymerizing a monomer such as methyl(meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,n-nonyl (meth)acrylate, (meth)acrylic acid and glycidyl (meth)acrylate,a resin obtained by copolymerizing a plurality of these monomers,polyacrylonitrile and a copolymer thereof, polycyanoacrylate,polyacrylamide, and poly(meth)acrylate); a vinyl acetate- or vinylalcohol-based resin (e.g., vinyl acetate resin, polyvinyl alcohol,polyvinyl acetal-based resin, polyvinyl ether); a halogen-containingresin (e.g., vinyl chloride resin, vinylidene chloride resin,fluorine-based resin); a nitrogen-containing vinyl resin (e.g.,polyvinylcarbazole, polyvinylpyrrolidone, polyvinylpyridine,polyvinylimidazole); a diene-based polymerization product (e.g.,butadiene-based synthetic rubber, chloroprene-based synthetic rubber,isoprene-based synthetic rubber); polyethers (e.g., polyethylene glycol,polypropylene glycol, hydrin rubber, Penton resin); a resin ofpolyethylene-imines; a phenol-based resin (e.g., phenol·formalin resin,cresol·formalin resin, modified phenol resin, phenol·furfural resin,resorcin resin); an amino resin (e.g., urea resin, modified urea resin,melamine resin, guanamine resin, aniline resin, sulfonamide resin); anaromatic hydrocarbon-based resin (e.g., xyleneformaldehyde resin,toluene·formalin resin); a ketone resin (e.g., cyclohexanone resin,methyl ethyl ketone resin); a saturated alkyd resin; an unsaturatedpolyester resin (e.g., maleic anhydride-ethylene glycol polycondensate,maleic anhydride-phthalic anhydride-ethylene glycol polycondensate); anallyl phthalate resin (for example, a resin obtained by crosslinking anunsaturated polyester resin with diallyl phthalate); a vinyl ester resin(for example, a resin obtained by crosslinking a primary polymer havinga highly reactive acryl double bond at the terminal and having abisphenol A-type ether bond in the main chain, with styrene, acryl esteror the like); an allyl ester resin; polycarbonate; a polyphosphoric acidester resin; a polyamide resin; a polyimide resin; a silicone resin (forexample, a silicone oil such as polydimethylsiloxane, a silicone rubber,a silicone resin and a reactive silicone resin having in the molecule ahydrosiloxane, hydroxysiloxane, alkoxysiloxane or vinylsiloxanestructure and being curable by a catalyst or heat); a furan resin; apolyurethane resin; a polyurethane rubber; an epoxy resin (for example,those using a condensate of bisphenol A with epichlorohydrin, acondensate of novolak-type phenolic resin with epichlorohydrin, or acondensate of a polyglycol with epichlorohydrin); a phenoxy-type resin;and modified products thereof. One of these may be used alone, or two ormore of the resins may be used in combination.

These polymer materials each may have a low molecular weight or a highmolecular weight or may be in the form of oil, rubber or cured productand this may be arbitrarily selected according to the purpose for whichthe material is used and the environment.

Among these, more preferred are an unsaturated polyester resin, anacrylic resin, a methacrylic resin, a vinyl ester resin, an epoxy resinand a silicone resin.

The polymer material is also preferably an oily substance. The greaseobtained by mixing the particulate alumina and an oil not only followsthe unevenness of a heating element and a heat radiator but also cannarrow the space therebetween to more enhance the heat-radiating effect.

The oil which can be used is not particularly limited and a known oilcan be used. Examples thereof include a silicone oil, a petroleum-basedoil, a synthetic oil and a fluorine-based oil.

The particulate alumina of the present invention can be mixed with aceramic raw material such as glass to prepare a composition and, ifdesired, subjected to shaping, calcining and the like.

The surface of the particulate alumina in the present invention ispreferably coated with a surface-treating agent. For thesurface-treating agent, a silane coupling agent, a compound having anyone or more group selected from the group consisting of an amino group,a carboxyl group and an epoxy group, or a modified silicone oil is used.

When the surface-treated particulate alumina is kneaded with a resin,the content of the particulate alumina in the composition can beincreased as compared with the case where a surface-untreatedparticulate alumina is kneaded with a resin. Furthermore, even when theamount of the particulate alumina contained in the composition isincreased, increase in the viscosity of the kneaded product isrelatively small and the flexibility of the composition is less lost, sothat the composition can be enhanced in the machine resistance or thelike.

The silane coupling agent may be sufficient if it has a hydrolyzablesubstituent such as halogen atom or alkoxy group on the silicon atom,and a known compound can be used. Preferred examples thereof includevinyltrichlorosilane, vinyltrimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane,γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane,γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane,n-hexyltrimethoxysilane, n-octyltrimethoxysilane,n-dodecyltrimethoxysilane, phenyltriethoxysilane,diphenyl-dimethoxysilane and hexamethyldisilazane. One of these may beused alone, or two or more of the compounds may be used in combination.

The compound having one or more group of an amino group, a carboxylgroup and an epoxy group is preferably a compound capable of readilyadsorbing or reacting on the surface of particulate alumina under theaction of such a group, and a known compound can be used.

Preferred examples thereof include 1,2-epoxyhexane, 1,2-epoxydodecane,n-hexylamine, n-dodecylamine, p-n-hexylaniline, n-hexylcarboxylic acid,n-dodecylcarboxylic acid and p-n-hexylbenzoic acid.

As for the modified silicone oil, preferred examples thereof includeKF-105, KF-101, KF-102, X-22-173DX, KF-393, KF-864, KF-8012, KF-857,X-22-3667, X-22-162A, X-22-3701E (all are produced by Shin-Etsu ChemicalCo., Ltd.), TSF4700, TSF4701, TSF4702, TSF4703, TSF4730*, TSF4770,TSE3070 (all are produced by GE Toshiba Silicones Co., Ltd.), SF8417,BY16-828, BY16-849, BY16-892, BY16-853, BY16-837, SF8411, BY16-875,BY16-855, SF8421, SF8418 and BY16-874 (all produced by Toray Dow CorningSilicone). One of these may be used alone, or two or more of themodified silicone oils may be used in combination.

The method for coating such a compound on the particulate alumina is notparticularly limited and a known method may be used. Examples thereofinclude a dry processing method and a wet processing method.

The coverage of the silane coupling agent or the like on the particulatealumina is preferably from 0.05 to 5 mass % based on the particulatealumina. If the coverage is less than 0.05 mass %, the coating effect isdifficult to obtain, whereas if the coverage exceeds 5 mass %, thecontent of unreacted silane coupling agent or the like increases andthis is disadvantageous, for example, in that such a compound remainsunreacted as an impurity.

When the composition of the present invention is formed into a sheet orgrease and inserted between the heat-generating portion of an electroniccomponent or semiconductor device and the high thermally conductivecomponent or plate, the heat generated can be efficiently dissipated andthe electronic component or semiconductor device can be prevented fromheat deterioration or the like and thereby reduced in failure rate orfavored with a prolonged life. The electronic component or semiconductordevice is not particularly limited, but specific examples thereofinclude CPU (central processing unit) of computers, PDP (plasmadisplay), energy devices (for example, lead storage battery, secondarybattery and capacitor) or peripheral equipment thereof (for example, ina hybrid electric vehicle, a device of providing the thermallyconductive composition between the secondary battery and the heatradiator to control the temperature and thereby stabilize batteryproperties), a heat radiator of electric motors, a Peltier element, aninverter and a (high) power transistor super-luminosity LED. Also, thecomposition is used by filling it in a glass frit for the purpose ofenhancing the strength of a ceramic substrate (LTCC (low-temperatureco-fired ceramic substrate)) or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing cumulative frequency distribution of theparticulate alumina obtained in Example 1.

FIG. 2 is a scanning electron microphotograph of the alumina particleobtained in Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in greater detail below by referringto Examples and Comparative Examples, however, the present invention isnot limited to these Examples.

EXAMPLE 1

To 100 parts by mass of commercially available alumina (produced byShowa Denko K.K.; average particle size: 3.08 μm), 200 parts by mass ofaluminum hydroxide (produced by Showa Denko K.K., average particle size:1.1 μm), 5 parts by mass of ammonium chloride, 2 parts by mass ofanhydrous aluminum fluoride and 2 parts by mass of boric acid were addedand mixed. The mixture was charged in a calcination vessel andheat-treated at maximally 1,500° C. for a residence time of 3 hours in atunnel kiln. The heat-treated product was taken out from the calcinationvessel and disintegrated by an air grinder. The particle sizedistribution of the disintegrated product was measured using sodiumhexametaphosphate as a dispersant by laser diffraction particle sizedistribution measuring apparatus Microtac HRA Particle Size Analyzermanufactured by Nikkiso Co., Ltd. FIG. 1 shows the particle sizedistribution. Also, the shape of the particulate alumina was observed bya scanning electron microscope (SEM). FIG. 2 shows the SEM photograph.

In order to evaluate the filling property in rubbers or plastics, 400parts by mass of the disintegrated product obtained after disintegrationwas blended with 100 parts by mass of silicone oil (a 1:1 blend ofTSE3070(A) and TSE3070(B) produced by GE Toshiba Silicones Co., Ltd.),mixed and further mixed for 5 minutes by a centrifugal defoaming andmixing device at 750 rpm. The viscosity of the obtained composition at25° C. was measured as the silicone viscosity by a Brookfield-typeviscometer.

Also, 250 parts of the alumina disintegrated product was blended with100 parts by mass of epoxy resin and mixed by a chemistirrer whilesetting the rotation to High Speed 3 and after allowing the mixture tostand at 25° C. for 2 hours, the viscosity was measured as the epoxyviscosity by a Brookfield-type viscometer. The evaluation results areshown in Table 1.

EXAMPLE 2

Evaluations were performed in the same manner as in Example 1 except forusing a commercially available calcined alumina (produced by Showa DenkoK.K., average particle size: 1.48 μm) as the alumina starting material.

EXAMPLE 3

Evaluations were performed in the same manner as in Example 1 except forusing a commercially available calcined alumina (produced by Showa DenkoK.K., average particle size: 5.24 μm) as the alumina starting material.

EXAMPLE 4

Evaluations were performed in the same manner as in Example 1 except forusing the same alumina starting material as in Example 1 and addingthereto ammonium chloride and aluminum fluoride at a ratio shown inTable 1.

EXAMPLE 5

Evaluations were performed in the same manner as in Example 4 except forusing boric acid in place of aluminum fluoride in Example 4.

COMPARATIVE EXAMPLE 1

Evaluations were performed in the same manner as in Example 1 except fornot adding ammonium chloride.

COMPARATIVE EXAMPLE 2

Evaluations were performed in the same manner as in Example 1 except fornot adding aluminum fluoride and boric acid.

COMPARATIVE EXAMPLE 3

Evaluations were performed in the same manner as in Example 1 except fornot adding aluminum hydroxide. TABLE 1 Comparative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 1Example 2 Example 3 Alumina (parts by 100 mass) Average particle 3.081.48 5.24 3.08 3.08 3.08 3.08 3.08 size (μm) Aluminum hydroxide 200 —(parts by mass) Average particle 1.1 — size (μm) Ammonium chloride 5 5 55 5 — 5 5 (parts by mass) Aluminum fluoride 2 2 2 4 — 2 — 2 (parts bymass) Boric acid (parts 2 2 2 — 3 2 — 2 by mass) Baked.disintegratedproduct Average particle 5.6 3.8 7.4 6.4 4.9 4.7 2.7 3.1 size (μm) Epoxyviscosity (P) 3,350 6,250 3,800 3,400 4,020 8,750 18,250 14,500 Siliconeviscosity 3,360 5,160 3,720 3,440 4,130 8,550 16,950 13,550 (P) Particleshape rounded rounded rounded rounded rounded amorphous particles notamorphous particles particles particles particles particles particleshaving particles where a part rounded having of particles shape, wherecutting edges have cutting agglomerated edges particles are present

INDUSTRIAL APPLICABILITY

According to the production method of the present invention, a roundedparticulate alumina of 10 μm or less can be industrially produced at alow cost. The rounded particulate alumina produced by the productionmethod of the present invention shows excellent fluidity and when filledin resins such as rubber and plastic, can ensure reduced viscosity andhigh filling efficiency, so that this rounded particulate alumina can beexpected to provide a compounded material having high thermalconductivity. TABLE 1 Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Example 5 Example 1 Example 2 Example 3Alumina (parts by 100 mass) Average particle 3.08 1.48 5.24 3.08 3.083.08 3.08 3.08 size (μm) Aluminum hydroxide 200 — (parts by mass)Average particle 1.1 — size (μm) Ammonium chloride 5 5 5 5 5 — 5 5(parts by mass) Aluminum fluoride 2 2 2 4 — 2 — 2 (parts by mass) Boricacid (parts 2 2 2 — 3 2 — 2 by mass) Baked.disintegrated product Averageparticle 5.6 3.8 7.4 6.4 4.9 4.7 2.7 3.1 size (μm) Epoxy viscosity (P)3,350 6,250 3,800 3,400 4,020 8,750 18,250 14,500 Silicone viscosity3,360 5,160 3,720 3,440 4,130 8,550 16,950 13,550 (P) Particle shaperounded rounded rounded rounded rounded amorphous particles notamorphous particles particles particles particles particles particleshaving particles where a part rounded having of particles shape, wherecutting edges have cutting agglomerated edges particles are present

1. A method for producing a particulate alumina, comprisingheat-treating (calcining) a composition comprising alumina, an aluminahydrate, ammonium chloride and a halogen compound other than ammoniumchloride and then disintegrating the heat-treated product.
 2. Theproduction method of a particulate alumina as claimed in claim 1,wherein the halogen compound other than ammonium chloride is a fluorinecompound or a boron-fluorine compound.
 3. The production method of aparticulate alumina as claimed in claim 2, wherein the fluorine compoundis at least one member selected from the group consisting of AlF₃, NaF,CaF₂, MgF₂ and Na₃AlF₆.
 4. A method for producing a particulate alumina,comprising heat-treating (calcining) a composition comprising alumina,an alumina hydrate, ammonium chloride and a boron compound and thendisintegrating the heat-treated product.
 5. A method for producing aparticulate alumina, comprising heat-treating (calcining) a compositioncomprising alumina, an alumina hydrate, ammonium chloride, a halogencompound other than ammonium chloride, and a boron compound thendisintegrating the heat-treated product.
 6. The production method of aparticulate alumina as claimed in claim 4, wherein the boron compound isat least one member selected from the group consisting of B₂O₃, H₃BO₃,mNa₂O·nB₂O₃ (m and n each represents an integer of 1 or more,hereinafter the same) and a boron-fluorine compound.
 7. The productionmethod of a particulate alumina as claimed in claim 1, wherein theparticulate alumina has a rounded shape having no cutting edge.
 8. Theproduction method of a particulate alumina as claimed in claim 1,wherein the composition is previously granulated before heat-treating(calcining) the composition.
 9. The production method of a particulatealumina as claimed in claim 1, wherein the alumina hydrate is at leastone member selected from the group consisting of an aluminum hydroxide,an alumina gel and a partially hydrated aluminum compound.
 10. Theproduction method of a particulate alumina as claimed in claim 1,wherein the average particle size of the particulate alumina is 10 μm orless.
 11. The production method of a particulate alumina as claimed inclaim 10, wherein the average particle size of the particulate aluminais from 0.3 to 8 μm.
 12. A resin composition comprising a particulatealumina produced by the production method as claimed in claim 1, and apolymer compound.
 13. The resin composition as claimed in claim 12,wherein the polymer compound is at least one member selected from analiphatic resin, an unsaturated polyester resin, an acrylic resin, amethacrylic resin, a vinyl ester resin, an epoxy resin and a siliconeresin.
 14. The resin composition as claimed in claim 12, wherein thecontent of the particulate alumina is 70 mass % of more.
 15. The resincomposition as claimed in claim 12, wherein the particulate alumina iscoated with a surface-treating agent.
 16. The resin composition asclaimed in claim 15, wherein the surface-treating agent is a silanecoupling agent.
 17. The resin composition as claimed in claim 15,wherein the surface-treating agent is a compound having any one or moregroup selected from the group consisting of an amino group, a carboxylgroup and an epoxy group.
 18. The resin composition as claimed in claim15, wherein the surface-treating agent is a modified silicone oil. 19.The resin composition as claimed in claim 15, wherein the coverage ofthe surface-treating agent is from 0.05 to 5 mass % based on theparticulate alumina.
 20. A ceramic composition comprising a particulatealumina produced by the production method as claimed in claim
 1. 21. Anelectronic component or semiconductor device comprising the resincomposition as claimed in claim
 12. 22. A CPU or PDP comprising theresin composition as claimed in claim
 12. 23. A peripheral equipment forbatteries, or a peltier element, an inverter or a power transistor,comprising the resin composition as claimed in claim 12.